1. Field of the Invention
The present invention relates to electro-optical device substrates, active matrix substrates, and methods for inspecting the electro-optical device substrates.
2. Description of Related Art
Hitherto, liquid crystal display devices formed by a pair of substrates holding a liquid crystal therebetween have been known. Concerning these liquid crystal display devices, a display device in which an active matrix substrate is used as one of the pair of substrates has been put to practical use. Regarding the active matrix substrate, a plurality of data lines and a plurality of gate lines, the gate lines intersecting the data lines at right angles, are formed on a glass sheet or the like. A pixel electrode is formed in accordance with the intersection of each data line and each gate line. Each pixel electrode is connected via a thin-film transistor to each data line and each gate line.
The number of gate lines and data lines to be formed corresponds to the number of display pixels. For example, concerning a color liquid crystal display device, one type with 480 gate lines and 640xc3x973 (corresponding to the RGB colors) data lines and another type with 1024 gate lines and 1280xc3x973 data lines are known. Since it is necessary to form a large number of wires on the active matrix substrate, defective data lines and gate lines, such as broken or narrowed lines (portion where the wire is narrower than the other portions), are not permitted.
In reality, however, it is impossible to prevent wire defects from occurring at a certain rate in manufacturing processes of active matrix substrates due to various causes. Hence, there is a demand for positive detection of an active matrix substrate having a defective gate line or a defective data line and for accurate determination of the location of a breakage so as to prevent a defect, i.e., the breakage, which arises from the same cause, from recurring.
To this end, a breakage inspection method is disclosed in Japanese Unexamined Utility Model Publication No. 63-70596.
In this breakage inspection method, concerning a plurality of gate lines formed in a stripe arrangement on a substrate, adjacent gate lines (or data lines) are connected at ends thereof. Specifically, a first gate line and a second gate line are connected at left ends thereof, the second gate line and a third gate line are connected at right ends thereof, the third gate line and a fourth gate line are connected at left ends thereof, the fourth gate line and a fifth gate line are connected at right ends thereof, and so forth. With this arrangement, a single wire is formed by series connection of gate lines. By detecting whether a predetermined current flows through this wire, it is determined whether any defective gate line is present.
This breakage inspection method can inspect whether there is any defective gate line, but fails to inspect the specific location of a defective gate line. Therefore, with this inspection method, it fails to determine the location of a broken gate line and to pursue or infer by analogy a cause that has given rise to the defect. Hence, the inspection method has a drawback in that it is impossible to take effective steps to prevent breakages from recurring.
In the above breakage inspection method, the presence of a defect can be determined by allowing a predetermined current i to pass through the series connected wire and measuring a potential difference across both ends of the wire. Specifically, a voltage when no defect is present in any part of the wire is measured beforehand. This voltage is expressed by iNRL where RL represents a resistance value per line in the wire (such as the gate lines) and N represents the total number (such as the total number of the gate lines) of the wire.
Next, the potential difference across both ends of the wire to be inspected is measured. When a defect is present in any part of the wire, the measured voltage is expressed by i(RB+NRL) where RB represents a resistance value at the location of a defect, such as the narrowed portion or the like. Then, a difference between these voltages, that is, iNRLxe2x88x92i(RB+NRL), is obtained. When the resultant detected voltage is smaller than the predetermined value, it is determined that some portion of the wire is broken.
With this method, the voltage computed from the above equation is ≈0 when NRL greater than  greater than RB. It is therefore impossible to perform defect detection. Specifically, the above method has a drawback in that, when the number of wires is great (that is, when the resistance NRL is great) or when the wire is narrowed but not completely broken (that is, when the resistance RB is relatively small under a condition where the wire is partially narrowed), it is difficult to perform defect detection.
In order to eliminate the above drawbacks, a method described hereinafter has been proposed to detect breakages or narrowed portions. This method is described with reference to FIG. 6. In an active matrix substrate S2 shown in FIG. 6, for example, a Y shift register 31, operating as a gate electrode drive circuit, and a buffer stage 33 are provided at left ends of gate lines (G1 to G6). A Y shift register 32 and a buffer stage 34 are provided at right ends.
In this inspection method, output levels of final stages of the buffer stage 34 on the side of the Y shift register 32 are set at a low level, and a selection pulse is input to the Y shift register 31. Specifically, output signals from final-stage inverters of the buffer stage 33 on the side of the Y shift register 31 are switched one after another from a low level to a high level. As a result, currents i1, i2, . . . i6 flow through the gate lines G1, G2, . . . G6 in order. By measuring each current value in the vicinity of the buffer stage 34, the method inspects the gate lines one by one for the presence of breakages.
If each of the current values of the currents i1, i2, . . . i6 is not smaller than a predetermined value, it is determined that no gate line is broken. In contrast, when the measured current value is not greater than the predetermined value, it is determined that the gate line is somehow defective.
When the Y shift registers 31 and 32 and the like are formed with polysilicon prepared by a low-temperature process having a maximum process temperature of about 400 to 600xc2x0 C., it is known that there is a high risk that the Y shift registers 31 and 32 experience electro-static damage and malfunctioning is thereby caused. Furthermore, defective patterning may be caused due to an effect of particles and the like, thus causing malfunctioning in the Y shift registers 31 and 32.
Hence, when at least one of the Y shift registers 31 and 32 is defective and all of the buffer stages 33 and 34 are set at a high level, no current can pass through the gate lines (G1 to G6) by serially selecting the gate lines using the above breakage inspection method. Therefore, there is a fear of being unable to always perform breakage inspection in a stable manner using the above breakage inspection method.
In addition, in the above breakage inspection method, a large number of wires must be selected one after another for detecting the presence of breaks. Thus, the method has a drawback in that it requires a long period of time for inspection.
Accordingly, it is an object of the present invention to provide an electro-optical device substrate, an active matrix substrate, and a method for inspecting the electro-optical device substrate for quickly and accurately specifying the location of a defect and for always performing defect inspection in a stable manner.
To this end, according to one aspect of the present invention, there is provided an electro-optical device substrate including a plurality of wires, a plurality of switching devices, and a power-supply means. The switching devices are interposed between each of the adjacent wires. Each of the switching devices belongs to a first group or a second group. The adjacent switching devices belong to different groups. The switching devices belonging to the groups are switched on/off in units of each group. The power-supply means passes a current through pairs of wires connected in series via the switching devices or applies a voltage to the pairs of wires.
In another aspect of the present invention, there is provided a method for inspecting the above electro-optical device substrate. The method is for inspecting an electro-optical device substrate having a plurality of wires and a plurality of switching devices, interposed between each of the adjacent wires. The method divides the switching devices into a first group and a second group so that the adjacent devices belong to different groups. The method includes a first wire inspection step of switching on the switching devices belonging to the first group and allowing a current to pass through pairs of wires connected in series via the switching devices or applying a voltage to the pairs of wires, thus determining the presence of a defect in the pairs of wires; a second wire inspection step of switching on the switching devices belonging to the second group and allowing a current to pass through pairs of wires connected in series via the switching devices or applying a voltage to the pairs of wires, thus determining the presence of a defect in the pairs of wires; and a defect determining step of determining a defective wire based on the determination result of the first wire inspection step and the determination result of the second wire inspection step.
According to the method for inspecting the electro-optical device substrate, the presence of a defect in the pairs of adjacent wires can be determined. Hence, it is possible to quickly detect the presence of a defective wire. Also, since it is possible to determine the presence of a defect in the pairs of wires connected in series by the switching devices belonging to the first group and the presence of a defect in the pairs of wires connected in series by the switching devices belonging to the second group, a defective wire can be specified in a relatively detailed manner based on the determination results.
In another aspect of the present invention, there is provided an electro-optical device substrate including a plurality of wires, each wire including a first end and a second end; a plurality of first switching devices interposed near the first end between each of the adjacent wires, in which each of the first switching devices belongs to one of a first group and a second group, the adjacent switching devices belong to different groups, and the switching devices belonging to the groups are switched on/off in units of each group; a plurality of second switching devices interposed near the second end between each of the adjacent wires, in which each of the second switching devices belongs to one of a third group and a fourth group, the adjacent switching devices belong to a different group, and the switching devices belonging to the groups are switched on/off in units of each group; a first power-supply means for allowing a current to pass through a plurality of pairs of wires connected in series via the first switching devices or for applying a voltage to the pairs of wires; and a second power-supply means for allowing a current to pass through a plurality of pairs of wires connected in series via the second switching devices or for applying a voltage to the pairs of wires.
In another aspect of the present invention, there is provided a method for inspecting the electro-optical device substrate. The method divides the first switching devices into a first group and a second group so that the adjacent first switching devices belong to different groups. The method has an inspection step of performing one of a first step and a second step. The first step includes a first wire inspection step of switching on the switching devices belonging to the first group and allowing a current to pass through pairs of wires connected in series via the switching devices or applying a voltage to the pairs of wires using the second power-supply means, thus determining the presence of a defect in the pairs of wires; and a second wire inspection step of switching on the switching devices belonging to the second group and allowing a current to pass through pairs of wires connected in series via the switching devices or applying a voltage to the pairs of wires using the second power-supply means, thus determining the presence of a defect in the pairs of wires. The second step includes a first wire inspection step of switching on the switching devices belonging to the third group and allowing a current to pass through pairs of wires connected in series via the switching devices or applying a voltage to the pairs of wires using the first power-supply means, thus determining the presence of a defect in the pairs of wires; and a second wire inspection step of switching on the switching devices belonging to the fourth group and allowing a current to pass through pairs of wires connected in series via the switching devices or applying a voltage to the pairs of wires using the first power-supply means, thus determining the presence of a defect in the pairs of wires. This inspection method further includes a defect determining step of determining a defective wire based on the determination result of the first wire inspection step and the determination result of the second wire inspection step.
According to the method for inspecting the electro-optical device substrate, even when one of the first power-supply means and the second of the power-supply means functions incorrectly, the other power-supply means can be used to perform inspection. It is therefore possible to always perform inspection in a stable manner.
In the above electro-optical device substrate, each of the first power-supply means and the second power-supply means may be a circuit operable as a driving (or driving device) means for the wires. Specifically, each power-supply means may include a shift register for serially shirting data commanding each wire to be driven and 3-state buffers each corresponding to each stage of the shift register. An output terminal of each 3-state buffer may be connected to an end of each wire. With this arrangement, it is not necessary to provide an additional wire-inspection circuit, thus reducing the manufacturing cost.
In another aspect of the present invention, there is provided an electro-optical device substrate including a plurality of wires formed by alternately arranging individual first wires and individual second wires; a plurality of switching devices interposed between each of the first wires and each of the second wires which are adjacent to each of the first wires at one side; and a power-supply means for allowing a current to pass through pairs of wires connected in series via each of the switching devices or for applying a voltage to the pairs of wires.
In another aspect of the present invention, there is provided a method for inspecting the electro-optical device substrate. The method includes a wire inspection step of switching on the plurality of switching devices and allowing a current to pass through a plurality of pairs of wires connected in series via the switching devices or applying a voltage to the pairs of wires, thus determining the presence of a defect in the pairs of wires.
According to the method for inspecting the electro-optical device substrate, it is possible to determine the presence of a defect in the pairs of wires conducted in series. Thus, there is an advantage in that it is possible to promptly perform detailed wire inspection.